Spiral Matrix Traversal in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the starting row index for spiral traversal.

DSA C

int top = [1];

Drag options to blanks, or click blank then click option'

A-1

B0

C1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Setting top to 1 instead of 0 causes skipping the first row.

Using negative indices which are invalid in C arrays.

The top row index starts at 0 because array indices in C start from 0.

2fill in blank

medium

Complete the code to move the left boundary right after traversing the left column.

DSA C

left[1];

Drag options to blanks, or click blank then click option'

A++

B--

C+=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using -- decreases left, moving boundary left instead of right.

Using -= or += without a value causes syntax errors.

After traversing the left column, we move the left boundary right by incrementing it.

3fill in blank

hard

Fix the error in the loop condition to traverse the top row from left to right.

DSA C

for (int i = left; i [1]= right; i++) {
    printf("%d ", matrix[top][i]);
}

Drag options to blanks, or click blank then click option'

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < excludes the last element in the top row.

Using > or >= causes the loop to never run or run incorrectly.

The loop should include the right boundary, so use <= to go from left to right inclusive.

4fill in blank

hard

Fill both blanks to correctly traverse the right column from top to bottom.

DSA C

for (int i = [1]; i [2] bottom; i++) {
    printf("%d ", matrix[i][right]);
}

Drag options to blanks, or click blank then click option'

Atop + 1

Btop

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at top repeats the corner element already printed.

Using < excludes the bottom row element.

Start from the row below top (top + 1) and go up to bottom inclusive (using <=).

5fill in blank

hard

Fill all three blanks to correctly traverse the bottom row from right to left.

DSA C

for (int i = [1]; i [2] [3]; i--) {
    printf("%d ", matrix[bottom][i]);
}

Drag options to blanks, or click blank then click option'

Aright - 1

Bright

C>=

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at right repeats the corner element.

Using > excludes the leftmost element.

Using left as a value instead of a variable causes errors.

Start from one left of right (right - 1), go while i is greater than or equal to left, decrementing i.

Practice

1. What is the main idea behind Spiral Matrix Traversal?

easy

A. Traverse only the diagonal elements of the matrix

B. Traverse the matrix row by row from top to bottom

C. Traverse the matrix column by column from left to right

D. Traverse the matrix in a circular pattern from outer to inner layers

Solution

1. Step 1: Understand traversal pattern

   Spiral traversal means moving around the edges of the matrix and gradually moving inward in a circular way.

2. Step 2: Compare options

   Only Traverse the matrix in a circular pattern from outer to inner layers describes moving in a circular pattern from outer to inner layers, which matches spiral traversal.

3. Final Answer:

   Traverse the matrix in a circular pattern from outer to inner layers -> Option D

4. Quick Check:

   Spiral traversal = circular outer to inner [OK]

Hint: Think of peeling an onion layer by layer [OK]

Common Mistakes:

• Confusing spiral with row-wise traversal
• Thinking spiral means diagonal traversal
• Ignoring the inward movement after outer layer

2. Which of the following C code snippets correctly initializes variables for spiral traversal of an m x n matrix?

easy

A. int top = 0, bottom = m-1, left = 0, right = n-1;

B. int top = m-1, bottom = 0, left = n-1, right = 0;

C. int top = 0, bottom = n-1, left = 0, right = m-1;

D. int top = n-1, bottom = m-1, left = 0, right = 0;

Solution

1. Step 1: Identify correct boundary initialization

   For spiral traversal, top starts at 0, bottom at last row (m-1), left at 0, right at last column (n-1).

2. Step 2: Match with options

   int top = 0, bottom = m-1, left = 0, right = n-1; matches this initialization exactly; others swap or mix row and column indices incorrectly.

3. Final Answer:

   int top = 0, bottom = m-1, left = 0, right = n-1; -> Option A

4. Quick Check:

   Boundaries = top=0, bottom=m-1, left=0, right=n-1 [OK]

Hint: Top and left start at 0; bottom and right at max index [OK]

Common Mistakes:

• Swapping m and n in bottom or right
• Starting top or left at max index
• Confusing row and column boundaries

3. What is the output of the following C code snippet for spiral traversal of a 3x3 matrix?

int matrix[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
int top=0, bottom=2, left=0, right=2;
while(top <= bottom && left <= right) {
  for(int i=left; i<=right; i++) printf("%d ", matrix[top][i]);
  top++;
  for(int i=top; i<=bottom; i++) printf("%d ", matrix[i][right]);
  right--;
  if(top <= bottom) {
    for(int i=right; i>=left; i--) printf("%d ", matrix[bottom][i]);
    bottom--;
  }
  if(left <= right) {
    for(int i=bottom; i>=top; i--) printf("%d ", matrix[i][left]);
    left++;
  }
}

medium

A. 1 4 7 8 9 6 3 2 5

B. 1 2 3 6 9 8 7 4 5

C. 1 2 3 4 5 6 7 8 9

D. 1 3 5 7 9 2 4 6 8

Solution

1. Step 1: Trace first outer layer traversal

   Top row left to right: 1 2 3; then right column top to bottom: 6 9; bottom row right to left: 8 7; left column bottom to top: 4.

2. Step 2: Move inward and print center

   Now top=1, bottom=1, left=1, right=1; print center element matrix[1][1] = 5.

3. Final Answer:

   1 2 3 6 9 8 7 4 5 -> Option B

4. Quick Check:

   Spiral order = 1 2 3 6 9 8 7 4 5 [OK]

Hint: Follow boundaries and print edges clockwise [OK]

Common Mistakes:

• Skipping center element
• Mixing row and column indices
• Not updating boundaries correctly

4. Find the error in this spiral traversal code snippet for a 3x3 matrix:

int top=0, bottom=2, left=0, right=2;
while(top < bottom && left < right) {
  for(int i=left; i<=right; i++) printf("%d ", matrix[top][i]);
  top++;
  for(int i=top; i<=bottom; i++) printf("%d ", matrix[i][right]);
  right--;
  for(int i=right; i>=left; i--) printf("%d ", matrix[bottom][i]);
  bottom--;
  for(int i=bottom; i>=top; i--) printf("%d ", matrix[i][left]);
  left++;
}

medium

A. The variables top and bottom are swapped

B. The for loops should use < instead of <=

C. The while loop condition should use <= instead of <

D. The matrix indices are accessed incorrectly

Solution

1. Step 1: Analyze loop condition

   The condition top < bottom && left < right stops before the center element is processed in odd-sized matrices.

2. Step 2: Correct condition for full traversal

   Using <= allows the loop to run when top equals bottom or left equals right, ensuring center elements are included.

3. Final Answer:

   The while loop condition should use <= instead of < -> Option C

4. Quick Check:

   Use <= in while condition for complete spiral [OK]

Hint: Use <= in while to include center elements [OK]

Common Mistakes:

• Stopping traversal too early
• Changing for loop bounds incorrectly
• Swapping top and bottom variables

5. Given a 4x4 matrix:

int matrix[4][4] = {
  {1, 2, 3, 4},
  {5, 6, 7, 8},
  {9, 10, 11, 12},
  {13, 14, 15, 16}
};

Write the spiral traversal output if you start from the bottom-left corner and move clockwise inward.

hard

A. 13 9 5 1 2 3 4 8 12 16 15 14 10 6 7 11

B. 1 2 3 4 8 12 16 15 14 13 9 5 6 7 11 10

C. 13 14 15 16 12 8 4 3 2 1 5 9 10 11 7 6

D. 16 15 14 13 9 5 1 2 3 4 8 12 11 10 6 7

Solution

1. Step 1: Understand starting point and direction

   Start at bottom-left (matrix[3][0] = 13) and move clockwise: up, right, down, left, inward.

2. Step 2: Trace spiral clockwise from bottom-left

   Up column: 13 9 5 1; right row: 2 3 4; down column: 8 12 16; left row: 15 14 10 6; then inner spiral: 7 11.

3. Final Answer:

   13 9 5 1 2 3 4 8 12 16 15 14 10 6 7 11 -> Option A

4. Quick Check:

   Start bottom-left clockwise spiral = 13 9 5 1 2 3 4 8 12 16 15 14 10 6 7 11 [OK]

Hint: Change start and direction, then trace edges inward [OK]

Common Mistakes:

• Starting from top-left instead of bottom-left
• Moving counter-clockwise instead of clockwise
• Mixing row and column indices